Neutrophils make up 50% to 70% of white blood cells. There are many reasons for low neutrophil percentage, including physiological low, infections, hematologic disorders, hypersplenism, autoimmune disorders, and so on. 1. Physiologic low: Children between the ages of 4 and 14 have low neutrophil percentages. 2. Infections: Viral infections such as influenza virus, gram-negative bacilli such as typhoid fever or paratyphoid fever, and protozoan infections such as malaria increase the depletion of neutrophils and produce substances that affect the production of neutrophils, resulting in a low percentage of neutrophils. 3. Blood system diseases: Aplastic anemia, paroxysmal sleep hemoglobinuria and other blood system diseases cause neutrophil production and maturation disorders, resulting in a low percentage of neutrophils, often accompanied by a decrease in platelets and red blood cells. 4. Hypersplenism: hypersplenism caused by liver cirrhosis and portal hypertension causes a large number of neutrophils to remain in the spleen and increase destruction, resulting in a low percentage of neutrophils in the blood. 5. Autoimmune diseases: autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis can affect the blood system, and autoantibodies can destroy neutrophils, resulting in a low percentage of neutrophils. Low neutrophil percentages can also be associated with physical and chemical damage such as radiation, medications such as aspirin, and nutritional deficiencies. A low neutrophil percentage alone does not mean anything and requires prompt medical attention to determine the cause of the disease in conjunction with the clinical signs and symptoms and to make a definitive diagnosis.